Base stations having antenna arrays have been widely used in cellular networks for directional signal transmission and reception with an increased gain compared to an omni-directional antenna. The increased gain translates into a higher cell density and data throughput. An antenna array needs to be calibrated across its sub-array paths to remove any linear phase and/or amplitude distortions (hereafter simply referred to as phase distortion) in these paths. If the transmission beam pattern is out of phase or otherwise phase-distorted, the signal transmitted by the base station at normal transmission power may not be correctly received and decoded by a wireless device, e.g., a user terminal. To compensate for the phase distortions, the base station may transmit data at a higher power level; however, increasing the transmission power acts as a load to the system, causing a reduction to the power that can be allocated to other wireless devices. In addition, the signal transmitted at higher power may interfere with other terminals, causing a reduction in signal quality.
Calibration of the antenna array is typically performed by careful coordination of radio signals transmitted by the sub-arrays of an antenna array. Coordination of the radio signals transmitted by the sub-arrays requires signal correction or compensation, which in turn requires estimation of impulse responses of the sub-array paths (i.e., transmit or receive paths). Estimation of the impulse responses of the sub-array paths is normally done using centralized processing in a radio unit where the correction and compensation is done. In this regard, commonly owned and assigned U.S. patent application Ser. No. 13/894,826, entitled METHOD AND APPARATUS FOR ANTENNA ARRAY CALIBRATION USING TRAFFIC SIGNALS, which was filed May 13, 2013, discloses systems and methods for calibrating an antenna array using a centralized architecture.
Base stations for advanced 4th Generation (4G) and 5th Generation (5G) wireless, or cellular, networks require many radio units and many antennas. Further, it is important for base stations in these 4G and 5G wireless networks to be scalable and modular in order for the base stations to be cost effective and manageable. One issue with a centralized approach for estimating the impulse responses of the sub-array paths in such a base station is that a complexity of the centralized approach increases as the number of radio units (or sub-array paths) increases. This increases the cost and complexity of the base station.
As such, there is a need for systems and methods for estimating impulse responses of sub-arrays paths in a base station having an antenna array that enhance scalability and modularity of the base station without increasing the complexity of the base station.